The present invention relates generally to energy storage systems, and more particularly, to a battery network with compounded connections.
While the use of electricity, instead of gasoline, to power vehicles has been known for many years, electric vehicles (EVs) have started to become increasingly popular in recent years. For example, December 1996 marked the debut of General Motor""s EV1 electric vehicle.
One of the most critical components to the overall performance of an EV is the energy storage system, which provides the power necessary to operate the vehicle. A typical energy storage system for an EV includes a battery pack comprising one or more batteries that are electrically connected together in a certain configuration to provide desired performance characteristics. Most prior art EV energy storage systems focus on high voltage, high current solutions to providing the necessary power to the EV. The underlying assumption behind these prior art attempts is that in order to provide the power to move an EV at the desired speeds, relatively high current levels are required. The EV1, for example, includes a battery pack consisting of 26 Valve-Regulated Lead Acid (VRLA) modules electrically connected together in a single series string for an available voltage of 312 Volts and a storage capacity of about 16.3 kW.
As shown in FIG. 1, other similar prior art approaches involve connecting a number of monolithic component batteries 2 in a single series column 4 and connecting a couple of such columns 4 at each end of the column in parallel to reach the desired total pack voltage.
There are, however, a number of significant disadvantages associated with these prior art approaches. For example, a battery pack constructed as a single series string is inherently susceptible to high failure rates, because the failure of any individual battery component in the pack automatically results in total battery pack failure (or the failure of the entire respective column of batteries) through an open circuit as no current flow can occur through the pack during either discharge or re-charge of the battery pack.
Additionally, the performance of a battery pack comprising component batteries connected together as a single series string is limited by the weakest battery in the string, both during discharge and re-charge. During discharge, the current delivery capacity of the entire battery pack is limited to that of the individual component battery with the lowest capacity in the string. Likewise, during charging of the battery pack, the individual component battery with the lowest capacity reaches a state of full charge first, and limits the re-charging of the entire battery pack.
Moreover, the individual component battery within such battery pack with the lowest capacity is over-discharged during each discharge cycle and over-charged during each charge cycle. Both of these conditions are damaging to battery capacity and cycle life. Thus, the normal cycling of a battery pack constructed a single series string provides an inherently unstable situation in which the weakest component batteries tend to become weaker still, converging toward failure of these members and, ultimately, the entire battery pack.
Furthermore, the EV1 battery pack draws a high level of current through each of the individual component batteries in series. As a result, a higher depth of discharge (DOD) is required during operation, which adversely affects the cycle life of the individual component batteries and the battery pack as a whole.
In addition to the operational disadvantages associated with the prior art battery packs, there are also some significant structural disadvantages. For example, the EV1 battery pack weighs 1175 lbs and thus is a significant component of the overall weight of the EV, negatively impacting the potential range of the vehicle before needing recharging.
Consequently, a need exists for an improved energy storage system, and more particularly for an improved battery operating system for EVs.
The present invention, therefore, provides an improved battery operating system for EVs designed to overcome the disadvantages described above. An array of individual component batteries are connected in compounded series and parallel connection to form a battery network. In accordance with the present invention, a battery network is formed by construction of a two- or three-dimensional array of individual batteries. The battery network thus formed comprises sufficient individual batteries connected in series so that the series voltage of the individual node batteries sum to the desired overall battery package voltage. In addition, the battery network thus formed comprises sufficient individual batteries connected in parallel so that parallel connection of individual node batteries sums the current delivery capacity to the desired overall battery package current delivery capacity.
In one embodiment, an X by Y two-dimensional array of individual battery components is formed by connecting each node battery in the array to its nearest neighbor nodes with both series and parallel connections using an electrically conductive material. The array of individual component batteries is configured to provide a two-dimensional battery network having X columns and Y rows. Each column in the network includes Y batteries electrically connected in series to form a string of batteries. Each of the X columns or strings are then further electrically connected together in parallel, to produce a network of X columns of batteries connected together in parallel, each of the X columns having Y batteries connected together in series. Finally, each of the individual component batteries is further configured with compound interconnections, such that each of the individual component batteries are connected in parallel with all adjacent individual component batteries in the same row.
These and other features and advantages of the present invention will be appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings.